DESCRIPTION
MASTR II Base Station, 406 to 512 megahertz receivers
are single conversion, superheterodyne FM receivers designed
for one-through eight-frequency operation. The solid state
receiver utilizes integrated circuits (ICs), monolithic crystal
filters and discrete components with each of the crystal filters
located between gain stages to provide 100 dB selectivity and
maximum protection from de-sensitization and intermodula-
tion.
The receiver consists of the following modules:
•
RF Assembly (Includes Mixer)
•
IF-Filter
•
Oscillator/Multiplier (Osc/Mult)
•
IF/Audio and Squelch (IFAS)
•
Optional Ultra-High Sensitivity
(UHS) Pre-Amplifier
Audio, supply voltages and control functions are con-
nected to the system board through P903 on the Osc/Mult
board, and P904 on the IFAS board. The regulated +10 Volts
is used for all receiver stages except the audio PA stage which
operates from the A+ system supply.
Centralized metering jack J601 on the IFAS board is pro-
vided for use with Test Set 4EX3A11 or Test Kit 4EX8K12.
The test set meters the oscillator, multiplier, IF Detector and
IF amplifier stages. Speaker high and low are metered on the
system board metering jack.
A block diagram of the complete receiver is shown in
Figure 2.
Refer to the appropriate Maintenance Manual for complete
details on each receiver module listed in the Table of Contents.
MAINTENANCE
DISASSEMBLY
To service the Receiver from the top (see Mechanical Parts
Breakdown):
1. Pull the locking handle down, then pry up the top cover
at the front notch and lift off the cover.
To service the Receiver from the bottom:
1. Pull the locking handle down and pull the radio out of
the mounting frame.
2.
Remove the top cover, then loosen the two bottom cover
retaining screws and remove the bottom cover (see Fig-
ure 1).
3. To gain access to the bottom of the Osc/Mult and IFAS
board, remove the six screws (A) holding the receiver
bottom cover (see Figure 3).
To remove the OSC/Mult board from the radio:
1. Remove the six screws (A) holding the receiver bottom
cover.
2. Remove the eight screws (E) holding the IF-Filter bottom
cover.
3. Remove the four screws (B) holding the board.
4. Press straight down on the plug-in Osc/Mult board from
the top to avoid bending the pins when unplugging the
board from the system board jack.
To remove the IFAS board from the radio:
1. Remove the six screws (A) holding the bottom cover, and
the one screw (C) holding the board.
2. Remove the two screws (D) holding the audio PA
heatsink to the right side rail.
Refer to Figure 4 for receiver module location.
NOTE
Figure 2 - Receiver Block Diagram
Figure 1 - Disassembly Procedure
(Top View)
LBI-38505 LBI-38505
2
(3 pages)
(197 pages)
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